The sensors are connected to specially designed semiconductors (players include Microsoft, which acquired chipmaker Canesta last year, and smaller companies such as PrimeSense). The chips take the information collected by the sensor and, using computer algorithms, produce a series of 3-D images mirroring your movements.

A recent Supreme Court decision, confusing Copyright Office rules and Amazon's Kindle policies all indicate that the only way consumers will ever get to resell "used" ebooks may be to sell their hard drives, too. More